bending wood

hi guys,

one more problem....
i am trying to build a speaker using curved sides a la Wilson Benech Act Two and Sonus Faber Amati see link below

http://www.hifi-notes.com/sonusfaberamatifabrikage-nl.htm

I have built the bracing (actually I cut out 18mm MDF in the shape I wanted) and tried to bedn 8mm and 6mm MDF sheet but it did not work. 4mm MDF sheet works but to get a 25mm thick cabinet one would need 6 sheets of 4mm and that might end up lookng like plywood and worse still actine like plywood.

I have 6 18mm MDF braces per cabinet. The top and bottom are 30mm MDF.

1. how does one bend MDF?
2. is there an alternative to bending MDF?

Regards
Navin
 
Actually.......

the 4mm mdf is probably the best way to go.

If you have a look at "Windswept" and "Tulip" on my web site, you will see some eg's of what can be done. (they actually use 3mm mdf)

ok, there is the problem with the edge showing, but there must be a way around that, you are not leaving it raw anyway!!

as to "sounding" like ply, i can assure you that it will not !!!
If you laminated the layers with pva type glue, spread on evenly over the whole of both surfaces using a paint brush, you be amazed at just how NON-resonant they become very quickly !! The 4.5" Tulip uses only 3 layers of 3mm mdf, and if you tap the outside of it, all you get is the dull thud of much thicker flat mdf.

Go with the 4mm mdf, try it after you have say 4 layers on, and see what you think !! you can always add the extra later if you really feel you need to.

Oh !! and have fun, it ain't easy !!!

AG
 
I'm not sure if this can help at all, but once I've seen a guy doing curve chairs with plywood for a boat that he was building.

his method was the following:

- make a steel frame with the shape of the bent wood final.

-insert the strait plywood panel in the steel frame and squeez it.

- the frame was filled with water. I dunno if it is on the beginnig or the end of the process.
 
I suggest to cut the MDF like this:

Inside

|xx|__|xx|__|xx|__|xx|__|xx|__|xx|__|xx|
|xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx|

Outside

You can use a saw with the correct depth or a router.
Try several depths and widths to see which one is the best. I have used this idea with plywood for another project (not a speaker box) and it worked fine. It should work with MDF.
 

roddyama

diyAudio Moderator Emeritus
2002-01-19 9:25 am
Michigan
I would try ply wood over MDF. I fear that the MDF will try to separate as you glue more on layers. It is not very strong in that way. There are layers in the structure of MDF that are not as strong as a glue bond.

Take a look at this site. These guys make Hedlund horn copies by bending and bonding layers of plywood on a form. The last layer is the venier. Beautiful work!:p
http://hornet.hi-fi.hr/Pics.htm
Select "Details from Production"

Just a note: try to find marine or aircraft grade, void free plywood. That should keep you from getting any seams or holes.

As Andy says, "...have fun, it ain't easy !!!"
Rodd Yamas***a
 

Two Moons

Member
2001-12-06 10:47 am
Bending Wood

Navin,

I am going to make some speakers like the ones you have planned. My inspiration were the Sonus speakers you provided the link to. Laminating multiple layers of plywood or thin MDF will give you tremendous strength, especially if bent. Search the knowledge base at www.woodweb.com and maybe ask questions in a forum. There are many experienced woodworkers there who have a lot of experience with the bending of many types of wood.

Good luck with your project and post pictures of it when ready. I'd like to see how someone elses turns out before I get my feet wet.

Dave
 
At a plywood store or good home fixup place they have 4x8 panels of stuff that is 1/2 " particle board ripped about every 1/4" as Francois described. BUT it is glued to a piece of high quality birch veneer (on one side only)

Amazing stuff- it will bend to a 4" radius. Only in one direction
I was thinking about making an open baffle with 4" radius edges
on the sides by filling the cracks with glue. That's a lot of glue though! I think it will be very rigid when it dries(if ever)
It would be best to use glue with fibers mixed in-maybe just sawdust. Best to use ribs to set the shape first-they could be removed if necessary.

You mentioned that many layers would be like plywood-I don't think so. But, even plywood in that shape would be fine I'll bet.

Look at the Sonus fabers-they are made from solid wood, which is supposed to be bad, but the shape makes them work I'll bet.
 
At a boating store you can get different things to mix with the resin to make it thick-microballons, chopped fiber, etc.
especially if they sell West System stuff.
My concern with this is the cost-epoxy is pricy, but maybe the quantities aren't as great as I was thinking. hmmmmmm
I've also got a plan to use Sonotubes in a new way- still have to try it though.
 
well there are 2 ways from the way I see it.

1. use 4mm MDF and use multiple layers (6 in my case). I would then bond 5 layers to make 20mm MDF then add the lead (3mm) and then add the last layer.

2. use 18 or 25mm MDF but break it into vertical strips and use toungue and grove joints. This way the sides will be made of many vertical strips (maybe as many as 6) then cover the strips with lead sheet (3mm, cover that with 4mm MDF and lastly cover that with veneer. I am using teh 4mm MDF as a shield so my son (born April 4th 2002) accidently does not get his hands on the lead as he begins to crawl.

I prefer version 1 it looks easier. Tongue and groove joints are really tough and even then you cant bend 18mm MDF at all. believe me I tried it it cracked.

once the layers are done then I would add a 6mm frame to cover the edges. the front and back woould "sit" on this frame.

My internal dimension are 8". My external dimensiion will be about 10.5" (8"+54mm) at the front and might max out to 11" at the widest point. My wife has a 12" limit to my speakers. She also mentioned a 4 foot height and 18" depth. She gets smarter on ways to limit the size of my boxes each time.

BTW Andy did you see the post of my Audio Concpets, SS 8546, SS9900 speakers and also my electroinics?

Regards
Navin
 

roddyama

diyAudio Moderator Emeritus
2002-01-19 9:25 am
Michigan
Navin,

The resin will adhere to the MDF.

One word of caution. Don't apply the fiber glass and resin in your basement or any where in the house. The fumes will permeate everything (even the food in your refrigerator). I learned this from a friends experience.

Rodd Yamas***a
 
crazier idea

4mm MDF
3mm fiberglass matting bonded in resin
4mm MDF
3mm fiberglass mating in resin
4mm MDF
3mm fiberglass mating in resin
4mm MDF
3mm fiberglass mating in resin
4mm MDF
3 mm lead
4mm MDF

thickness of panel (6 x 4mm + 5 x 3mm) = 39mm.

will this work. is it worth the trouble. remember my drivers are rather ordinary (Vifa TC series).

watered down version of above....
20mm (5 layers of 4mm MDF) MDF
3mm lead
4 mm MDF
3mm fiberglass bonded in resin
thickness = 30mm I can then sand the fiberglass and paint it any colour.

Regards
Navin